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Inspired by the photosynthesis process found in plants, scientists at Caltech have developed an electrically conductive film that may help pave the way for creating devices that use solar power to split water into hydrogen fuel.
When applied to semiconducting materials such as silicon, the group's nickel oxide film prevents rust buildup and facilitates an important chemical process in the solar-driven production of fuels such as methane or hydrogen.
The film was developed at the Joint Center for Artificial Photosynthesis (JCAP). Commenting on the group's work, Nate Lewis, the George L. Argyros Professor and professor of chemistry at Caltech and a coauthor of a new study, published this week in the online issue of the journal the Proceedings of the National Academy of Sciences, described the film, saying, "We have developed a new type of protective coating that enables a key process in the solar-driven production of fuels to be performed with record efficiency, stability, and effectiveness, and in a system that is intrinsically safe and does not produce explosive mixtures of hydrogen and oxygen."
Outdoing the leaf
The goal is to develop safe, efficient artificial photosynthetic systems—also called solar-fuel generators or "artificial leaves"—that replicate the natural process of photosynthesis.
The artificial leaf that Lewis' team is developing consists of three main components: two electrodes—a photoanode and a photocathode—and a membrane. The photoanode uses sunlight to oxidize water molecules to generate oxygen gas, protons, and electrons, while the photocathode recombines the protons and electrons to form hydrogen gas. The membrane, which is typically made of plastic, keeps the two gases separate in order to eliminate any possibility of an explosion, and lets the gas be collected under pressure to safely push it into a pipeline.
The team has shown that its nickel oxide film is compatible with many different kinds of semiconductor materials, including silicon, indium phosphide, and cadmium telluride. When applied to photoanodes, the nickel oxide film far exceeded the performance of other similar films—including one that Lewis's group created just last year. That film was more complicated—it consisted of two layers versus one and used as its main ingredient titanium dioxide (TiO2, also known as titania).
While some crucial elements to the puzzle have been found, Lewis cautions that scientists are still a long way off from developing a commercial product that can convert sunlight into fuel. Other components of the system, such as the photocathode, will also need to be perfected.
To see inside the lab, you can check out this video about the JCAP's work.
Will work continue?
Some unfortunate news: while the team has made some major breakthroughs, it is threatened with a lack of funding. The research center was initially funded in 2010 by the U.S. government as one of a handful of U.S. Department of Energy Innovation Hubs, according to an article on the subject that appeared this week in Technology Review. You can see more about that coverage here.
You can also learn more about the group's work in this recent press release.